Technologies employed for early detection of diseased tissue (e.g., cancer) include visual inspection, x-ray computer tomography, ultrasound, positron emission tomography (PET) scanning, magnetic resonance imaging (MRI) and so on. While such technologies have had various degrees of success detecting disease in an early stage, improvements are constantly being sought. Definitive diagnosis, especially of malignant disease, still typically includes biopsy, an invasive, costly, time-consuming procedure.
It is possible to obtain quantitative information on the physical characteristics of a material through ultrasound inspection. Non-destructive ultrasonic testing has been employed for evaluating engineering structures by the determination of their relevant material properties. Translating this approach to biomedical applications (e.g., disease screening) is complicated due to the lack of appropriate theoretical models that facilitate reconstructing physical properties of biological tissue. In particular, models derived from the conventional mechanics of solids, including biological domains, are based on a continuum representation. The continuum representation postulates the existence of a typical dimension or Representative Volume Element (RVE), below which matter may be assumed to be continuous and fully homogeneous. On these foundations, mechanical phenomena may then be represented in a differential equation format. This modeling strategy breaks down when it is not possible to establish a continuum RVE. Establishing a continuum RVE is not possible when phenomena are examined on a length scale at which the discrete, inhomogeneous nature of the media is evident, as frequently encountered in biological tissue examination.
Approaches have been developed that attempt to address these concerns by representing complex composite domains as continua with continuum inclusions. These theories, collectively known as “micromechanics”, still suffer from the limitation that they do not incorporate the discrete nature of matter, while remaining computationally manageable at domain sizes that are currently incomparable to lattice dynamics, ab-initio approaches, or molecular dynamics.
Additionally, measuring mechanical properties of biological soft tissue has been elusive because tissue is not well-behaved material. Indeed, mechanically soft tissue is known as being inhomogeneous, anisotropic, non-linear, and viscoelastic.